In recent years, advances in technology, as well as ever-evolving tastes in style, have led to substantial changes in the design of automobiles. One of the changes involves the complexity of the electrical and drive systems within automobiles, particularly alternative fuel vehicles, such as hybrid, battery electric, and fuel cell vehicles. Such alternative fuel vehicles typically use one or more electric motors, perhaps in combination with another actuator, to drive the wheels.
Such vehicles often use two separate voltage sources, such as a battery and a fuel cell, to power the electric motors that drive the wheels. Power electronics, such as direct current-to-direct current (DC/DC) converters, are typically used to manage and transfer the DC power from one of the voltage sources and convert to more or less voltage. Also, due to the fact that alternative propulsion automobiles typically include direct current (DC) power supplies, direct current-to-alternating current (DC/AC) inverters (or power inverters) are also provided to invert the DC power to alternating current (AC) power, which is generally required by the motors.
The power electronics units typically perform their respective function, at least in part, using one or more power switches or transistors, which are controlled by the vehicles control system. To insure the operating integrity of the electric drive system, a multi-layer monitoring system may be used to ensure that the output of the electric drive (torque, speed, etc.) is as requested, or possibly in the case of a fault situation, as delivered.
A commonly employed first layer monitoring system performs diagnostics on all sensor inputs. Such low level diagnostics may include checking whether a sensor is able to communicate or checking to see if a sensor reading is within its expected or allowable operating range. Such sensors (e.g., physical or virtual software replacements) may include current sensors, voltage sensors, position sensors, temperature sensors, and the like.
Often, a second layer monitors the control system to ensure that it is producing the intended outputs, such as the power switch duty cycles generated by the Pulse Width Modulation (PWM) system. A conventional method for checking the duty cycles is to essentially perform an entire redundant calculation. However, such a calculation demands considerable processing power and memory.
Accordingly, it is desirable to provide a method and system for performing second layer monitoring of the duty cycles used to control power electronics in automotive electrical systems. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent description taken in conjunction with the accompanying drawings and the foregoing technical field and background.